Land Use, Land-Use Change and Forestry

Other reports in this collection What Net Changes in Carbon Stocks from ARD Can Be Expected in the Future?

To estimate global potential carbon stock changes induced by ARD activities during the commitment period, Yamagata and Alexandrov (1999) used the land-use change scenarios obtained from the IMAGE 2.1 model (Alcamo et al., 1998). The model gives a total carbon stock at maturity of 216 t C ha-1, 142 t C ha-1, and 90 t C ha-1 for the low-, mid-, and high-latitude regions respectively (Yamagata and Alexandrov, 1999). These estimates are similar to those made by Dixon et al. (1994) for low- and mid-latitude (tropical and temperate forests) but very small compared to the high-latitude (boreal forests) carbon estimates of Dixon et al. (1994). The Yamagata and Alexandrov (1999) simulations lack the large soil carbon pools that have accumulated at high latitudes during the past 8,000 to 10,000 years. The simulations yield an emission rate of 1.8 Gt C yr-1 during the commitment period if the scenario of land-use changes suggested by Leemans et al. (1998) took place.

These estimates for global ARD fluxes would be significantly reduced, however, if the actual tree canopy cover (<<100 percent) of the ARD lands in each region is used. In general, higher thresholds (e.g., 40 percent) capture not only clearing but also forest degradation as a deforestation activity. Higher thresholds also credit more afforestation and reforestation activities on land already covered by trees. On the other hand, higher thresholds are not sensitive to conversions of open forests, giving no credit for establishing open forests and no debit for clearing them.

To illustrate how thresholds change the ARD potential, we simulated the global carbon fluxes from ARD activities during the first commitment period. We combined remotely sensed canopy cover data (Nemani and Running, 1997) with the carbon stock change model of Yamagata and Alexandrov (1999) and the land-use change model of Leemans et al. (1998). Each value is predicted assuming the Land Use definitional scenario, with a different canopy cover threshold (Table 3-18).

Table 3-18: Total estimates of carbon fluxes for Annex I countries during the first commitment period that would be induced by land-use change based ARD activities since 1990, in Gt C yr-1. Estimates for non-Annex I countries are given in parentheses to illustrate the carbon potentials for projects between Annex I and non-Annex I countries. Removals are shown as positive and emissions as negative numbers.

Tree Cover Threshold
in Forest Definition
All Forests
10% Canopy
40% Canopy
of Canopy Cover

(Gt C yr-1)
(Gt C yr-1)
Net flux
(Gt C yr-1)

The result demonstrates several implications for the Annex I countries. First, global carbon removals from ARD activities are as high as 0.2 Gt C yr-1. Second, a lower canopy cover threshold significantly reduces potential carbon removals from afforestation and reforestation activities and increases potential emissions from deforestation activities. Third, net carbon removals from ARD activities decline from 0.16 (40 percent cover threshold) to 0.06 Gt C yr-1 (10 percent cover threshold).

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